SIG Sauer MCX Rattler Canebrake .300 BLK AR Pistol, 5.5 in Barrel, Coyote/FDE, Adjustable Gas, SD-Length Handguard
This MCX Rattler Canebrake is the micro .300 AAC Blackout variant with a 5.5-inch barrel, Coyote/FDE Cerakote finish, and the MCX short-stroke gas piston system with adjustable gas. It features the extended SD-length M-LOK handguard with a long, non-bridging top Picatinny rail running most of the handguard’s length forward of the receiver’s rail, and the bufferless MCX recoil system that enables a true side-folding PCB arm brace. It comes with three 30-round PMAGs, flip-up sights, and an installed inert training device (suppressor-size shroud).
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: There are minimal markings from prior handling and use. Please refer to the photos for detailed views of the finish and components.
What’s Included
- Sig Sauer MCX Rattler Canebrake .300 BLK AR pistol (5.5-inch barrel)
- Inert training device (suppressor-size shroud), installed
- Flip-up sights, installed
- Three 30-round Magpul PMAG GEN M3 polymer magazines marked '300 BLK'
The Canebrake configuration pairs a 5.5-inch .300 AAC Blackout barrel with an extended SD-length aluminum M-LOK handguard and separate 1913 Picatinny top rail sections—a receiver rail and a long, non-bridging segment on the handguard—leaving an intentional gap for gas-system access/clearance. The SD handguard is designed to direct flash forward when unsuppressed, and this pistol includes an installed inert training device (suppressor-size shroud) sized to the handguard.
It uses the MCX short-stroke gas piston system with adjustable gas for suppressed or unsuppressed use, and a fast 1:5 twist suited to the caliber. The bufferless dual-spring MCX recoil system allows a true side-folding setup using the 1913 rear interface and PCB arm brace, keeping the package compact.
This micro-format Rattler balances portability and control, with an approximate factory overall length of 29.5 inches and weight around 6.0 lb. Capacity is 30+1 with the included 30-round magazines.
Controls and components include a two-stage, flat-blade match trigger and flip-up sights. The Coyote/FDE Cerakote finish is applied over a hard-coat anodized receiver. Markings include "SIG MCX MULTI-CALIBER" and "SIG SAUER INC., NEWINGTON NH USA" on the lower, "RATTLER" on the upper plate, and "MULTI-CAL" inside the dust cover. Made in the USA; MFG part number PMCX-300B-5B-TAP-CANE.